1. Field of Invention
This invention relates to data transmitting and receiving interface devices, and more particularly to those devices that utilize asynchronous serial electronic communication.
2. Description of Prior art
Communication among digital systems, personal computers, has become a necessity in recent years with the advent of local area computer networks and the world wide web. Much of this communication is done via telephone line, cable, optical, or radio media, so the information must be exchanged in a serial manner. That is, only one piece of information is exchanged at a time. Serial communication among digital systems requires the use of special interface equipment. A typical state of the art serial communication network is shown in FIG. 1. The special interface equipment includes Universal Asynchronous Receiver Transmitters (UARTS), and line drivers. A detailed description of the operation of this state of the art network is given below.
The digital systems communicate with their respective UARTs in a parallel manner using the parallel interfaces 30 31. In parallel communication, binary words are exchanged. A binary word consists of several, typically sixteen, binary digits (bits). In the parallel interface, bits are represented by voltage levels. A logic zero is typically represented by zero volts, and a logic one is typically represented by five volts. A separate wire is required for each bit. A typical parallel interface will, therefore, contain sixteen communication wires plus two or three control wires.
The UARTs communicate with their respective line drivers in a serial manner using the serial interfaces 32 33. In serial communication, bits are exchanged sequentially. That is, the sending UART breaks up a binary word into bits and sends one bit at a time. The receiving UART receives one bit at a time and combines the bits into binary words. The number of bits transmitted in a second is known as the baud rate. In a typical serial interface, the bits are represented by either voltage or current levels, and a typical serial interface will contain one or two communication wires and two or three control wires.
The line drivers communicate with each other via the communication medium 34. The sending line driver, first, converts each bit, received from its UART, into an appropriate voltage level, current, tone, light pulse, or radio frequency, and, then, sends the signal out over the communication medium. The receiving line driver, first, converts the received signal to a voltage level, and, then, sends this voltage level to the respective UART.
To summarize, a binary word is transferred from one digital system to another as follows. The sending digital system sends a binary word to the respective UART. The UART breaks up the binary word into bits and sends each bit, sequentially, to the respective line driver. The line driver converts each bit into an appropriate signal, and sends the signal out over the communication medium. The receiving line driver converts the received signal into a bit and sends this bit to the respective UART. The UART combines the bits into a binary word, and sends the word to the respective digital system. The receiving digital system receives the binary word.
This communication process is slow, since only one bit can be transferred at a time. A state of the art system operates at 56K baud, and this means that the transfer of a one megabit file would require at least eighteen seconds.
Several solutions have been proposed to increase the throughput of bits, but thus far, no solution has been proposed that would enable the serial transfer of more than one bit at a time.